1. Field of the Invention
The present invention relates to a method of making a color filter in which the color filter is formed on a glass substrate used in a color liquid crystal display device by using a color film sheet. In particular, the present invention relates to a method of making a color filter in which the transferability of the color filter onto a glass substrate is enhanced and deformations (curls) of a color film sheet during storage or use are prevented.
2. Description of the Related Art
FIGS. 9A and 9B are sectional views which show a method of making a color filter using a color film sheet that is generally used.
A color film sheet 40, shown in FIG. 9A, includes a base film 3 on which a light-heat conversion layer 4 and a color dye layer 2 are deposited in that order, and a color film sheet 50, shown in FIG. 9B, includes a base film 3 provided with a color dye layer 2 on one surface and a light-heat conversion layer 4 on another surface.
As the base film 3, a drawn resin such as polyethylene terephthalate (PET) is used. The color dye layer 2 is composed of a mixture of a resin binder and a pigment, and has any one of the colors R (red), G (green), and B (blue). One color film sheet 40 or 50 is provided with a color dye layer 2 having one color. Also, the light-heat conversion layer 4 is composed of a mixture of a resin binder and carbon powder, and generates heat by absorbing light.
As shown in FIGS. 9A and 9B, a transfer is performed by placing the color film sheet 40 or 50, provided with any one of color dye layers 2 among R (red), G (green), and B (blue), on a glass substrate 1. When light energy such as laser beams is selectively radiated onto the color film sheet 40 or 50 from above, the light-heat conversion layer 4 generates heat. The color dye layer 2 is melted by the heat to adhere to the glass substrate 1. Then, by peeling off the color film sheet 40 or 50, a transferred layer of the color dye layer 2 is formed on the glass substrate 1.
By transferring the respective color dye layers 2 of R, G, and B sequentially, a color filter in which each color is sequentially placed on the glass substrate 1 is formed.
In the color film sheet 40 shown in FIG. 9A, the light-heat conversion layer 4 is selectively irradiated with laser beams passing through the base film 3, and the laser beams are absorbed by the light-heat conversion layer 4. Heat-generation occurs only in the irradiated sections, and the color dye layer 2 is melted and transferred onto the glass substrate 1.
Also, in the color film sheet 50 shown in FIG. 9B, the light-heat conversion layer 4 absorbs laser beams first to generate heat, and the heat is transmitted through the base film 3 to the color dye layer 2. The color dye layer 2 is heated and melted to be transferred onto the glass substrate 1.
However, in the case of a transfer by means of heat produced by laser beams using the conventional color film sheet 40 or 50 as described above, with respect to the color film sheet 40 shown in FIG. 9A, the light-heat conversion layer 4 is transferred onto the glass substrate 1 along with the color dye layer 2 when the sheet 40 is peeled off. Also, with respect to the color film sheet 50 shown in FIG. 9B, the color dye layer 2 is not completely separated from the base film 3 when the color film sheet 50 is peeled off, and a portion of the color dye layer 2 remains on the base film 3, resulting in an incomplete transfer.
As a result, in the color filter produced, the black light-heat conversion layer partially remains on the transferred layers of the respective colors, or the transferred layers are not transferred in a clear pattern.
Also, since the base film 3 is composed of a resin such as PET, it has a relatively large thermal capacity. If the base film 3 is formed thickly, the heat generated by the light-heat conversion layer 4 is taken by the base film 3 during heating by laser beams. Thereby, the color dye layer 2 is not melted, is not transferred onto the glass substrate 1, and remains on the base film 3.
Because of the problems described above, the base film 3 must be formed as thinly as possible. However, if the base film 3 is formed thinly, the base film 3 will curl as shown in FIG. 10.
If the color film sheet 40 or 50 is left as a sheet, the surface of the color film sheet provided with the base film 3 will curl inward, resulting in a difficulty in bringing it into close contact with the glass substrate 1 during use.
Generally, the color film sheet 40 or 50 is stored, being wound in a roll, and it is drawn out up to an appropriate length and cut or not cut for use. In such a case, when the color film sheet 40 or 50 is drawn out, a similar curl to that described above occurs.
Therefore, there may be a difficulty in bringing the color film sheet 40 or 50 in close contact with the glass substrate 1, or wrinkling may occur on the color film sheet 40 or 50 if uncurling is attempted by force. As a result, it is not possible to transfer the color dye layer 2 clearly and surely onto the glass substrate 1, which is not practical.
The curling of the color film sheet 40 or 50 during storage presumably results from solvent components. To describe this in detail, since the light-heat conversion layer 4 is composed of a resin binder and carbon, a large amount of solvent components is contained, and since the color dye layer 2 is composed of a resin binder and a pigment, a large amount of solvent components is also contained. Therefore, the solvent components diffuse into the surface of the base film 3 on the side of the light-heat conversion layer 4, and expand. Specifically, since the surface of the base film 3 does not have high crystallinity, solvent components or the like are easily diffused into the surface, and thus a diffused surface layer easily expands. Therefore, the bottom face of the base film 3 elongates, and the top face of the base film 3 appears to shrink, resulting in a curl with the top face of the base film 3 turning inward.